Objectives: 1. To clarify the nature of the interactions between tissues and implanted materials used for orthopedic purposes. 2. To devise tests that quantify these interactions and allow predictive assessments of materials. 3. To devise new metals or improvements in presently used metals for minimizing the interactions. 4. To study clinical cases of interactions for assessment of in-service suitability of implants and reasons for failure. Methods: 1. Histological methods will be applied to animal and human (biopsy) material. 2. Metallurgical methods will be applied for study of corrosion (crevice fretting fatigue) at breakage and wear and for devising new materials and for testing same. 3. Coordinate study of used (usually failed) devices including 1 and 2 above, with the addition of clinical data (review of clinical reports including surgical descriptions, roentgenograms, etc.).